Add caching: the Spring cache abstraction, keys, eviction timing and the self-invocation trap

A Spring Boot 4.1.1 module whose test suite is the evidence for the article: 19 tests
producing 22 transcripts under docs/output/, plus 12 documentation chapters.

Findings the build pins:
- @EnableCaching has no exposeProxy attribute; the widely-copied
  @EnableCaching(exposeProxy = true) does not compile.
- Two methods sharing a cache name and an argument type share a key space, and one
  silently serves the other's answers.
- beforeInvocation = true is NOT deferred by TransactionAwareCacheManagerProxy on
  7.0.9 - doEvict picks evictIfPresent, which the decorator does not intercept.
- Four of five invalid declarations start a clean context and throw at the first call.
- Caffeine on the classpath silently displaces the simple provider.

caching/scripts/run-all.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# Regenerates every file under docs/output/.
+#
+#   ./scripts/run-all.sh
+#
+# Needs a JDK 25 and Maven 3.9. Everything except the two javap transcripts and the live
+# diagnostics dump comes out of the test suite, which is the point: the numbers in the article
+# are assertions that fail the build if they stop being true.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+echo "== test suite (transcripts 01-20)"
+mvn -B test
+
+echo "== javap transcripts (22)"
+./scripts/capture-bytecode.sh
+
+echo "== live diagnostics endpoint (23)"
+./scripts/capture-diagnostics.sh
+
+echo
+echo "docs/output:"
+ls -1 docs/output